The present invention relates generally to the field of high volume, high speed mailing machines for printing postage indicia on a succession of envelopes passing therethrough, and more particularly to such mailing machines having a digital ink jet printing device and an envelope flap closing and sealing device for closing and sealing the flaps of envelopes just prior to the printing operation.
Mailing machines of the type to which the present invention pertains have long been well known and have achieved a very high degree of commercial success. Mailing machines of this type typically include an elongate feed deck, an envelope conveyor mechanism extending along the feed deck, a hopper for holding a stack of envelopes with the flaps still open, a flap closing and sealing device located just downstream from the hopper, and a postage metering device mounted over the feed deck just downstream from the flap closing and sealing device. The postage meter typically includes an accounting device for monitoring the amount of postage used, and a printing device for printing a postage indicia on envelopes being conveyed along the feed deck. The postage meter further includes a postage amount setting mechanism for setting varying amounts of postage into the printing device, which is either a rotary drum holding a curved die on which the postage indicia is engraved, or a flat plate holding a flat die on which the postage indicia is engraved. In either case, each time an envelope is fed past the printing device, the die is inked by a suitable inking device and the ink is transferred to the envelope, either by rotation of the drum or by momentary pressure contact with the flat die.
Mailing machines utilizing this form of printing technology have worked quite well in various commercial applications despite certain drawbacks, such as mechanical complexity which entails a relatively high level of manufacturing and maintenance costs, limitations on the speed at which the machines can run due to the necessity of reinking the printing dies between each printing operation, and physical size and weight, which have also been a problem and the source of numerous customer complaints, particularly in professional offices where space is at a premium, since these machines tend to be rather large.
A significant technological breakthrough in the design and development of mailing machines of the type under consideration has been the development and refinement of digital ink jet printing technology over the past decade or so. To understand this, it must be understood that the printing of postage meter indicia on envelopes involves certain very critical characteristics. One is that, since a postage meter is, in effect, printing money in a specialized form, i.e., the postage indicia represents the payment to the U.S. Postal Service by the owner of the mailing machine for the privilege of having his mail delivered to an addressee, the quality of printing must be exceptionally high so that the indicia is visibly clear and devoid of any smudges and blurs for verification of authenticity and for mail sorting purposes, since genuine postage meter ink contains a die which is machine readable. Another characteristic is that the postage meter printing device must be highly reliable in operation and must print an acceptable indicia the first time on each envelope, since each printing represents the expenditure of money and therefore printings of inferior quality which must be discarded is commercially unacceptable. Thus, it has only been within the above mentioned time frame that ink jet technology has been refined and improved to the point where the quality of printing, speed of operation, and cost of manufacture and operation have become commercially acceptable for use in a mailing machine environment.
One of the major problems encountered in the development of a mailing machine utilizing the ink jet technology for printing the postage indicia, the solution to which the present invention is directed, is that of properly closing and sealing the flaps of envelopes traveling through the mailing machine which are of varying thickness. In the prior type of mailing machines discussed above, the envelopes traveled through the mailing machine on an elongate flat deck, the envelopes being conveyed along the deck by any suitable combination of rollers and/or belts. The deck was fixed in the mailing machine and the upper surface thereof defined a registration plane for the lower surface of the envelopes, referred to hereinafter as bottom registration. Varying thickness in the envelopes was accommodated by limited vertical movement of the printing die assembly in the postage meter. Thus, the typical forms of flap closing devices utilized in those machines was merely a strip of metal bent to a particular shape and forming an elongate blade, or alternatively a particularly shaped rod forming an elongate guide, the purpose in either case being to gradually urge the envelope flap through approximately a 90.degree. angle to cause it to pass through a suitable aperture in the deck and lie contiguous to the under surface of the rear panel of the envelope. During further movement of the envelope, it passed beneath a sealing roller which pressed the pre-moistened edge of the flap into contact with the rear panel with sufficient pressure to cause it to seal just prior to the envelope reaching the printing mechanism of the postage meter.
The significant factor of the bottom registration arrangement, as it relates to the present invention, is that the deck forming the registration plane is fixed, with the result that the rear panel of the envelope is always in the same plane, thereby permitting the flap closing device to be formed as a relatively simple, single piece, stationary element, since any variation in thickness of envelopes passing through the mailing machine is compensated for by movement of the printing die in the printing device of the postage meter, or by a short pressure deck under the die that could distort the envelope slightly during the printing cycle.
With printing devices utilizing ink jet technology, the situation is entirely different. Firstly, in order for the ink jet nozzles of any ink jet printer to deposit ink on the surface of the receiving medium, it is critical that a small predetermined gap be maintained between the exit plane of the nozzles and the surface of the receiving medium, typically in the order of one sixteenth to one thirty-second of an inch. This gap is necessary to achieve proper image quality, since too small a gap causes excessive ink to be deposited in the actual image area, and too large a gap results in too little ink being deposited, resulting in a blurred or fuzzy image. Thus, in the mailing machine environment, it becomes necessary to maintain this critical gap between the exit plane of the ink jet nozzles and the upper surface of the envelopes being conveyed through the mailing machine.
To accomplish this, the envelopes must be conveyed with the front panels on which the postage indicia is printing lying in a fixed registration plane, which is disposed beneath the exit plane of the nozzles a distance equal to the aforementioned gap. This arrangement is referred to hereinafter as top registration, as distinguished from the above described bottom registration in the prior mailing machines. The problem that arises, however, with top registration is that the plane of the rear panel of the envelopes is not fixed, as is the case with bottom registration, but rather must shift vertically in accordance with variations in the thickness of envelopes being conveyed through the mailing machine. Thus, in order for a flap closing device to operate effectively in this arrangement, the flap closing device must also shift vertically in synchronism with varying vertical positions of the rear panel of envelopes depending on the thickness of the envelopes.
Experience has shown that to redesign known flap closing devices that are fixed in prior mailing machines, since they are designed for bottom registration, to make them movable so as to shift vertically in synchronism with the varying positions of the rear panels of envelopes of varying thickness, would require a substantially complex mechanical and electronic design. It would, of course, be possible to provide a simple manual adjustment for the flap closing device which could be preset for varying thickness of envelopes, but this would require that all envelopes being fed through the mailing machine be of the same thickness, and this would so detract from the utility of the mailing machine as to render it virtually commercially unacceptable. Thus, even with top registration, the mailing machine must be capable of accepting envelopes of varying thickness in different batches of envelopes of the same thickness, or as mixed thickness within the same batch. To do this with conventional flap closing devices would require a sensing device to measure the thickness of each envelope passing through the mailing machine, which would have to be very accurate and have a rapid response time. The arrangement would also require some type of mechanical shifting mechanism that would be responsive to the sensing device and which would also have to operate very rapidly in order to shift the position of the flap closing device by the required amount for each successive envelope. It should be apparent that this arrangement would greatly increase the complexity of the flap closing device of the mailing machine, thereby substantially increasing the cost of manufacture and maintenance and decreasing the reliability and efficiency of operation, resulting in a product that is commercially less attractive than at present.
Thus, there is a substantial need for relatively simple, inexpensive and highly reliable flap closing device for envelopes of varying thickness being fed successively through a mailing machine which utilizes the top registration concept of positioning envelopes for proper printing.